1. Field of the Invention
The present invention relates to time duration or phase discrimination particularly with respect to a time duration or phase detector providing greater accuracy and resolution with accompanying simplicity than has heretofore been achieved in the art.
2. Description of the Prior Art
It is a desideratum in numerous technologies to provide precise time or phase discrimination in a stable and economical manner. For example, in the digital magnetic recording art utilizing READ/WRITE transducers recording on and reproducing from a moving magnetic medium, such as in discs, drums, tape and the like, a data pulse is often recorded by writing a flux transition that saturates the medium in one direction followed by the writing of a flux transition of the opposite polarity to saturate the medium in the opposite direction. Such a writing procedure may be utilized in the well known return-to-zero (RZ) magnetic recording format. When the conventional differentiating read head detects the recorded transition, a waveform approximating Lorentzian shape is generated having a peak of one polarity corresponding to the leading edge of the RZ pulse followed by a peak of the opposite polarity corresponding to the trailing edge of the RZ pulse. In the RZ format, the RZ pulse is representative of one of the binary data states.
Another conventional recording procedure utilizes the non-return-to-zero (NRZ) format wherein one of the binary data states is represented by an isolated flux transition. The read head in response to such a transition provides a waveform having a positive or negative peak depending on whether the write current saturated the medium from negative to positive polarity or from positive to negative polarity respectively.
In these and other recording formats, conventional positive and negative peak detectors provide signals upon the occurrences of the positive and negative peaks of the read waveforms. The opposite polarity peaks of the waveforms may be considered as first and second distinctive events respectively or as respective distinctive points of the waveforms.
In the magnetic recording technology as well as in other arts, information recorded is conveyed on the flux crossovers. It is often necessary to determine whether the time duration between the occurrences of two consecutive peaks of a readback waveform is greater than or less than a predetermined time interval. One type of prior art time duration discriminator utilizes a monostable multivibrator which is triggered to its astable state by the first occurring peak. The return of the monostable multivibrator to its stable state after its characteristic time interval has elapsed is compared to the occurrence of the second peak to provide the desired time interval discrimination. Typically, monostable multivibrator circuits are not sufficiently stable for precise and reliable time interval discrimination. Monostable multivibrators tend to be noise sensitive and do not always trigger at the same point with respect to the first peak. A wide bandwidth device is necessary since the triggering signal is often a steep wide bandwidth digital waveform.
Another prior art approach to time duration discrimination utilizes a high frequency counting technique. In such an approach the occurrence of the first peak starts a high frequency digital counter and the occurrence of the second peak stops the counter. The number of clock pulses counted in the interval provides a measure of the desired time duration. In order to attain time interval discrimination on the order of several nanoseconds, an accurate start/stop counter operating at an exceedingly high clock rate is necessitated to achieve the desired resolution. Such an approach tends to be exceedingly complex and hence expensive and at the present state of the digital oscillator and counter arts, this approach may not be realizable with available circuitry for nanosecond resolution.